Since the bacterial cellulose is edible as well as tasteless and odorless, it is utilized in the food industry. The homogenized bacterial cellulose's high dispersibility in water further provides it with many industrial applications, such as to maintain particle sizes of food, cosmetics or coating agents, to strengthen food materials, to maintain moisture, to improve stability of food, and to be used as low-calorie additives and an emulsion stabilizer.
The bacterial cellulose is characterized by a sectional width of its fibrils which is smaller by two orders of magnitude than that of other kinds of cellulose fibers such as those derived from wood pulp.
Owing to such structural and physical feature of fibril, a homogenized bacterial cellulose has plenty of industrial applications as a reinforcing material for polymers, especially hydrophilic polymers. Products prepared by solidification of the homogenized bacterial cellulose in the form of a lump or paper show a high elastic modulus in tension owing to the above feature, and are therefore expected to have excellent mechanical properties for use in various kinds of industrial materials.
However, since an aqueous suspension or dispersion of the homogenized BC contains solvent such as water in an amount of a few to a few hundreds times the amount of cellulose component, it has some disadvantages such as the increase of space for storage, increase of the costs for storage and transportation, and decomposition of cellulose by bacteria during storage.
It is known that the characteristic features of BC will be lost upon drying. This may be attributed mainly to the following reasons:
The fibrils of BC is so fine that its surface area per volume is large. Accordingly, when moisture is evaporated from BC upon drying, a strong agglutination originating in hydrogen bonds will occur between the fibrils. Once such agglutination has occurred, the hydrogen bonds formed between the fibrils can be hardly broken off even by the addition of water. As a result, it is very hard to restore the dried BC to the original homogenate suspended in water.
In order to solve the above problems, some methods have been already proposed, whereby aqueous BC suspension is freeze-dried or solvent is substituted for water in the aqueous BC suspension followed by drying so as to avoid the formation of the hydrogen bonds between the fibrils upon drying. However, it is also well known that the above methods need a huge amount of energy and complicated processes.
In order to solve the above disadvantages, the present inventors have already proposed a method for drying a bacterial cellulose, comprising adding a third component other than water and BC to the aqueous BC suspension and dehydrating and drying (Japanese Patent Application Hei 7 (1995)-329472). According to this method, the various properties of BC such as solubility, dispersibility, precipitation degree and viscosity may be restored when BC is returned from its dry state (water content is 25% by weight or less) to its original aqueous suspension.
The present inventors have further studied other methods for solving the above disadvantages, and found that the BC's various properties may be restored by dehydrating and drying BC under tension followed by homogenization even without adding the third components.